A construction worker lost a leg yesterday when a wall collapsed inside a historic Pioneer Square building under renovation, sending bricks and debris crashing down onto the man and a fellow workman.

Both men underwent surgery yesterday at Harborview Medical Center in Seattle. Firefighters recovered the leg and took it to the hospital, but surgeons were not able to reattach it.

The man whose leg was severed, a 26-year-old Auburn resident, was listed in critical condition late yesterday.

His co-worker, a 51-year-old Tacoma man, lost part of a leg but was in satisfactory condition.

The accident happened about 2 p.m. on the ground floor of the Buttnick building at First Avenue South and South Washington Street.

The men, employees of Turner Construction, were working inside on a scaffolding when the interior wall partly caved in, knocking the men off the structure, Fire Department spokeswoman Helen Fitzpatrick said. The men were quickly pulled from the rubble, she said.

The state Department of Labor and Industries was called to investigate the accident, Fitzpatrick said. A Turner manager at the scene declined to comment.

The old building, which used to house Buttnick Manufacturing and still bears the company's sign, has been gutted while undergoing renovation.

"The mortar in there is so old, it just falls apart," said one workman, who didn't give his name.

The building is being converted into office space and connected to offices in an adjoining five-story building, where Napoleon Cole and 15 employees run Fusion, a software company.

"We heard the building shake, and we thought that they were dropping something, like a crane was dropping something," Cole said. He ran to the roof to see ambulances arriving, and was advised to evacuate his building, he said.

Cole said that the Buttnick building suffers from age and was heavily damaged in the Nisqually earthquake in February 2001.